Some cyber security experts and privacy advocates said the massive attackreflected a flawed approach by the United States to dedicate more cyber resources to offence rather than defence, a practice they argued makes the internet less secure.

“Despite warnings, (NSA) built dangerous attack tools that could target Western software,” Mr Snowden said. “Today we see the cost.”

If @NSAGov had privately disclosed the flaw used to attack hospitals when they *found* it, not when they lost it, this may not have happened https://t.co/lhApAqB5j3

He said Congress should be asking the NSA if it is aware of any other software vulnerabilities that could be exploited in such a way.

“If [the NSA] had privately disclosed the flaw used to attack hospitals when they found it, not when they lost it, this may not have happened,” he added.

Hospitals have been partly blamed for not updating their software in March when a patch was released to fix the flaw. But Mr Snowden pointed out that had the NSA disclosed the vulnerability when it found it, hospitals would have had years to prepare, rather than months.